The present invention relates generally to storage containers for transporting articles, and particularly, to storage containers used in semiconductor fabrication facilities for transporting or storing wafers, and more particularly to storage containers having an indicator for detecting corrosive chemical elements.
A wafer has multiple microchips on its surface, and each chip has literally millions of devices and interconnection circuitry that are highly sensitive to contamination. As the feature size on a chip shrinks to accommodate higher performance and denser circuitry and the use of corrosion-prone copper, the need to control surface contamination becomes more critical. Contamination, which can come from many sources during wafer fabrication, such as particles, metals, and electrostatic discharge (ESD) often leads to a defective chip. The wafer fabrication process comprises many steps, such as patterning, deposition, etching, implantation or diffusion of metallic layers, dielectric layers or impurity elements on a semiconductor substrate. One such contamination comes from corrosive trace elements in the environment. Metal layers on a wafer exposed to the environment will often react with some trace elements in the environment such as, for example fluorine, chlorine, sulfur, and produce defects such as corrosion, metal pad discoloration, pad crystal defect, and metal fuse corrosion. For example, when copper corrosion occurs, the adhesion of the copper layer with other layers such as an inter-metal dielectric (IMD) of oxide is greatly affected. Killer defects are those causes of failure where the chip on the wafer fails during electrical test. Failure at electrical test results in a yield loss, causing the defective die on the wafer to be scrapped (thrown away) at a significant cost to the chip manufacturer. As device critical dimensions decrease, the problem of contamination becomes ever critical.
Until now, the preventative method is to store wafers in a controllable environment such as cleanrooms and minienvironments purged with an inert-gas like nitrogen, and to monitor the amount of trace elements with expensive measurement tools. However, corrosive trace elements come not only from the cleanroom environment, but may also come from the wafer container and wafer cassette themselves due to chemical outgassing or from residues left on the front side or backside of the wafer during IC processing. Storage of wafers in nitrogen-purged cleanrooms or minienvironments can only prevent external contamination but cannot stop contamination from within the wafer container itself.
For these reasons and other reasons that will become apparent upon reading the following detailed description, there is a need for a storage container for detecting the presence of corrosive chemical elements.